(PART-1)
PARADIGM (PAR-a-dime): 1) something serving as an example or model of how things should be done. 2) $ 0.20…
-Food Availability For Reef Animals
It has been known for some time that corals and other coral reef animals must feed. It is hard to get a good handle on the feeding dynamics of many reef animals. Interestingly enough, however, what we do know about feeding on a reef, as a whole, indicates that aquarists, generally, go about feeding their animals in the wrong way and with the wrong foods. By examining the types of available food, and the processes of feeding on a reef, I think it will become apparent that many of the problems we have with reef aquaria, such as excess nutrients, excessive growth of undesirable algae, and the inability to keep some animals alive and healthy is simply due to the feeding of inappropriate foods, compounded by feeding in the wrong manner.
Before I can discuss the major points of this proposition, however, I need to "set the stage" and discuss feeding in general, and explore a bit of what we know of reef food webs. Some of this information is the result of basic biological investigations, while other data come from some very nicely done ecological studies on the Great Barrier Reef.
-First Point: Animals Need To Feed.
All organisms need some sort of food; in fact, the ability to either feed or generate one's own food is probably a pretty decent criterion for describing life. Many organisms are photosynthetic; in other words, they absorb light and use that light energy to make chemicals. This production of chemicals using light energy is limited to those organisms that have chlorophyll in their bodies: photosynthetic bacteria (cyanobacteria), many types of algae, and plants. Photosynthetically-derived chemicals, which are mostly sugars, may be broken down, thereby releasing a portion of that absorbed light energy as chemical energy.
This secondary production of chemical energy, either in the initial organism that produced the sugar or in some other organism, is the basis for all basic energy utilization in all organisms. It is done by essentially the same chemical processes in all organisms, and this is one of the major reasons to consider all life as related. This process is called "respiration" and unlike the process that we normally associate with the term respiration, it really has nothing directly to do with breathing or gas exchange. Instead, it refers to the chemical breakdown and oxidation of sugar to release useable chemical energy in a cell.
The fact that this production of useable energy from the sugar is independent of the production of the sugar has some rather profound consequences. Because of this independence, the sugar may be broken down and used some distance away from where it is made and some time after it is made. This means that the organism that uses the sugar doesn't have to be the one that makes it. In other words, the development of the cellular biochemistry that allowed for the indirect utilization of light energy, allowed for the development of animals. Animals are organisms that don't have the photosynthetic machinery which is characteristic of the plants, algae, or cyanobacteria that comprise the primary producer trophic level in ecosystems. They must consume their food, and because of this they must either eat plants, plant byproducts, or other animals.
Most reef animals are eating small zooplankton that are gelatinous in nature. i.e. larvacean tunicate called Oikopleura. Unlike benthic tunicates, or sea squirts, larvaceans spend their entire lives as planktonic animals. They construct a transparent "house" (the edges of which are indicated by the arrows) out of mucus secreted by the epidermis of the animal's head. This house is about ¼ inch in diameter. In the house are the filters they use to collect food. The animal pumps water through the filters, and when they are full, the animal eats them, abandons the house and secretes a new house. It may do this several times an hour. Larvaceans, and old larvacean houses, are some of the most common, and nutritious of the gelatinous zooplankton (See Alldredge, 1972).
-Second Point: Animals Need To Feed On Organisms; They Don't Just Live On
Photosynthetic Byproducts.
Photosynthesis produces only sugars. It is the process of using light energy to fuse six carbon dioxide molecules and six water molecules together to make a simple sugar. In doing so, it gives off six oxygen molecules as a waste byproduct. Sugar is called a carbohydrate, because it contains only carbon, hydrogen and oxygen. Carbohydrates are useful and necessary chemicals; they may be burned for fuel, converted to fats or starches to store fuel, or fashioned into long chains as structural molecules such as cellulose and chitin. What they can't do, however, is be used to directly make a protein.
Proteins are the building blocks of all animal tissues, and the major components of all cells in all organisms. They are made of subunits called amino acids, often hundreds of them, fastened together in long chains. Amino acids, as their name implies, are molecules that have both an acid and an ammonia residue attached to them. Over 150 amino acids are found in nature, but the vast majority of proteins are made from only about 20 of them. This large number of amino acids may be hooked together in an almost endless variety of ways. And animal chemistry can build, remodel, and modify proteins wonderfully well. What animal chemistry cannot do is synthesize an ammonia group from nitrogen and hydrogen, nor can animals utilize nitrate or nitrite to form ammonia. This synthesis is largely done by bacteria or photosynthetic organisms.
Animals cannot manufacture amino acids from such basic chemical constituents as an ammonia or amine group and an organic acid, consequently, they must get them from some other source. Coral reef animals have one or two options for obtaining their amino acids. If they have zooxanthellae, they may get some amino acids from the zooxanthellae. Unfortunately, this is a zero-sum situation. As the zooxanthellae live within their host, any ammonia that they can utilize must come from their hosts' tissues as a waste product. If such ammonia is a waste product of the host, it is largely a byproduct of the host's metabolism or digestion. This means that the hosts always will require more amino acids, by a very large margin, than the zooxanthellae can provide. What the zooxanthella may do, however, is provide particular types of nitrogenous products unavailable elsewhere. However, even so, zooxanthellate animals must be getting their nitrogenous chemicals from another source, and that source is from feeding of one sort or another. Animals without zooxanthellae will not, of course, have this option. They simply must fulfill all of their needs from feeding.
Marine animals typically require that between five percent and 60 percent of the dry weight of the diet must be protein. For optimal growth of fish, the diet must be from 30 percent to 60 percent, depending on the fish. The absolute requirement from most inactive invertebrates is toward the lower end of the range, but for highly active invertebrates such as squids, it is likely as high as fish. All of this protein must come from either eating some other animal, alga, or plant; direct absorption from the water around the animal, or from a zooxanthellate symbiont. Direct absorption of dissolved amino acids is typically efficiently done in most marine invertebrates, however, there really is very little of this material available in natural systems. In a coral reef aquarium, however, this may be major source of amino acid accumulation by many animals. Production of amino acids by a zooxanthellate symbiont is of limited value, as most animals require a far larger amount of amino acids than may be available from this source. However, this latter source may provide some essential materials. Most amino acids, however, probably come from the assimilation of foods, including bacteria. Bacteria, in fact, are an important food for most benthic or bottom-dwelling marine animals. This is because bacteria have higher nitrogen to carbon ratios in their cells than do either typical animals, plants or algae. As a consequence many marine animals are specialized to eat bacteria, either directly out of the water column or indirectly as a frosting on sediment or detritus particles.
Protein is often a critical resource for animals. Farmers and aquaculturists have long known that one way to get maximum growth in captive animals is to make sure that they have access to a high protein diet. Such diets promote rapid growth and seem to foster generally good health in animals. Unfortunately, such diets are quite unnatural in coral reef areas.
(CONT. PART-2)
PARADIGM (PAR-a-dime): 1) something serving as an example or model of how things should be done. 2) $ 0.20…
-Food Availability For Reef Animals
It has been known for some time that corals and other coral reef animals must feed. It is hard to get a good handle on the feeding dynamics of many reef animals. Interestingly enough, however, what we do know about feeding on a reef, as a whole, indicates that aquarists, generally, go about feeding their animals in the wrong way and with the wrong foods. By examining the types of available food, and the processes of feeding on a reef, I think it will become apparent that many of the problems we have with reef aquaria, such as excess nutrients, excessive growth of undesirable algae, and the inability to keep some animals alive and healthy is simply due to the feeding of inappropriate foods, compounded by feeding in the wrong manner.
Before I can discuss the major points of this proposition, however, I need to "set the stage" and discuss feeding in general, and explore a bit of what we know of reef food webs. Some of this information is the result of basic biological investigations, while other data come from some very nicely done ecological studies on the Great Barrier Reef.
-First Point: Animals Need To Feed.
All organisms need some sort of food; in fact, the ability to either feed or generate one's own food is probably a pretty decent criterion for describing life. Many organisms are photosynthetic; in other words, they absorb light and use that light energy to make chemicals. This production of chemicals using light energy is limited to those organisms that have chlorophyll in their bodies: photosynthetic bacteria (cyanobacteria), many types of algae, and plants. Photosynthetically-derived chemicals, which are mostly sugars, may be broken down, thereby releasing a portion of that absorbed light energy as chemical energy.
This secondary production of chemical energy, either in the initial organism that produced the sugar or in some other organism, is the basis for all basic energy utilization in all organisms. It is done by essentially the same chemical processes in all organisms, and this is one of the major reasons to consider all life as related. This process is called "respiration" and unlike the process that we normally associate with the term respiration, it really has nothing directly to do with breathing or gas exchange. Instead, it refers to the chemical breakdown and oxidation of sugar to release useable chemical energy in a cell.
The fact that this production of useable energy from the sugar is independent of the production of the sugar has some rather profound consequences. Because of this independence, the sugar may be broken down and used some distance away from where it is made and some time after it is made. This means that the organism that uses the sugar doesn't have to be the one that makes it. In other words, the development of the cellular biochemistry that allowed for the indirect utilization of light energy, allowed for the development of animals. Animals are organisms that don't have the photosynthetic machinery which is characteristic of the plants, algae, or cyanobacteria that comprise the primary producer trophic level in ecosystems. They must consume their food, and because of this they must either eat plants, plant byproducts, or other animals.
Most reef animals are eating small zooplankton that are gelatinous in nature. i.e. larvacean tunicate called Oikopleura. Unlike benthic tunicates, or sea squirts, larvaceans spend their entire lives as planktonic animals. They construct a transparent "house" (the edges of which are indicated by the arrows) out of mucus secreted by the epidermis of the animal's head. This house is about ¼ inch in diameter. In the house are the filters they use to collect food. The animal pumps water through the filters, and when they are full, the animal eats them, abandons the house and secretes a new house. It may do this several times an hour. Larvaceans, and old larvacean houses, are some of the most common, and nutritious of the gelatinous zooplankton (See Alldredge, 1972).
-Second Point: Animals Need To Feed On Organisms; They Don't Just Live On
Photosynthetic Byproducts.
Photosynthesis produces only sugars. It is the process of using light energy to fuse six carbon dioxide molecules and six water molecules together to make a simple sugar. In doing so, it gives off six oxygen molecules as a waste byproduct. Sugar is called a carbohydrate, because it contains only carbon, hydrogen and oxygen. Carbohydrates are useful and necessary chemicals; they may be burned for fuel, converted to fats or starches to store fuel, or fashioned into long chains as structural molecules such as cellulose and chitin. What they can't do, however, is be used to directly make a protein.
Proteins are the building blocks of all animal tissues, and the major components of all cells in all organisms. They are made of subunits called amino acids, often hundreds of them, fastened together in long chains. Amino acids, as their name implies, are molecules that have both an acid and an ammonia residue attached to them. Over 150 amino acids are found in nature, but the vast majority of proteins are made from only about 20 of them. This large number of amino acids may be hooked together in an almost endless variety of ways. And animal chemistry can build, remodel, and modify proteins wonderfully well. What animal chemistry cannot do is synthesize an ammonia group from nitrogen and hydrogen, nor can animals utilize nitrate or nitrite to form ammonia. This synthesis is largely done by bacteria or photosynthetic organisms.
Animals cannot manufacture amino acids from such basic chemical constituents as an ammonia or amine group and an organic acid, consequently, they must get them from some other source. Coral reef animals have one or two options for obtaining their amino acids. If they have zooxanthellae, they may get some amino acids from the zooxanthellae. Unfortunately, this is a zero-sum situation. As the zooxanthellae live within their host, any ammonia that they can utilize must come from their hosts' tissues as a waste product. If such ammonia is a waste product of the host, it is largely a byproduct of the host's metabolism or digestion. This means that the hosts always will require more amino acids, by a very large margin, than the zooxanthellae can provide. What the zooxanthella may do, however, is provide particular types of nitrogenous products unavailable elsewhere. However, even so, zooxanthellate animals must be getting their nitrogenous chemicals from another source, and that source is from feeding of one sort or another. Animals without zooxanthellae will not, of course, have this option. They simply must fulfill all of their needs from feeding.
Marine animals typically require that between five percent and 60 percent of the dry weight of the diet must be protein. For optimal growth of fish, the diet must be from 30 percent to 60 percent, depending on the fish. The absolute requirement from most inactive invertebrates is toward the lower end of the range, but for highly active invertebrates such as squids, it is likely as high as fish. All of this protein must come from either eating some other animal, alga, or plant; direct absorption from the water around the animal, or from a zooxanthellate symbiont. Direct absorption of dissolved amino acids is typically efficiently done in most marine invertebrates, however, there really is very little of this material available in natural systems. In a coral reef aquarium, however, this may be major source of amino acid accumulation by many animals. Production of amino acids by a zooxanthellate symbiont is of limited value, as most animals require a far larger amount of amino acids than may be available from this source. However, this latter source may provide some essential materials. Most amino acids, however, probably come from the assimilation of foods, including bacteria. Bacteria, in fact, are an important food for most benthic or bottom-dwelling marine animals. This is because bacteria have higher nitrogen to carbon ratios in their cells than do either typical animals, plants or algae. As a consequence many marine animals are specialized to eat bacteria, either directly out of the water column or indirectly as a frosting on sediment or detritus particles.
Protein is often a critical resource for animals. Farmers and aquaculturists have long known that one way to get maximum growth in captive animals is to make sure that they have access to a high protein diet. Such diets promote rapid growth and seem to foster generally good health in animals. Unfortunately, such diets are quite unnatural in coral reef areas.
(CONT. PART-2)